I don't follow. In my build `-DCMAKE_INSTALL_SYSCONFDIR=/etc` is set already
Are you the one setting it or is the whatever tool you use maybe: `dh-cmake` defining them? It's not recommended to define this variables as absolute paths because it breaks `cmake --install --prefix` and cpack generators.
I don't think we should configure or define CFG_DIR; it should be evaluated from the install prefix according to the rules described above.
Uhm... `CFG_DIR` is something we use in code and it should be configurable.
It's configurable by evaluating the install prefix and the cfg_name but not setting it directly. Wasn't this also the case in Makefiles?